The 2016 Healthy Diet Score report by Csiro, the government’s science agency, canvassed the dietary habits of more than 86,500 adults across the country over a 12-month period.
With almost 47,000 additional surveys completed since then, that figure now stands at just 59 out of 100, confirming that Australian diets are worse than first thought.
An early snapshot of the survey results released in August last year awarded the nation's diet a score of 61 on a 100-point scale.
"We have an image of being fit and healthy, but with a collective diet score of 59/100 that image could be very different unless we act now," said Csiro research director Manny Noakes.
According to the 2016 Healthy Diet Score, 80% of respondents received an individual score below 70, the benchmark figure.
"If we can raise our collective score by just over 10 points, we help Australia mitigate against the growing rates of obesity and lifestyle diseases such as heart disease, type 2 diabetes and a third of all cancers," said Prof. Noakes.
"All people need to do is halve the bad and double the good. In other words, halve the amount of discretionary food you eat and double your vegetable intake."
People across Australia, in all occupations and age groups, were invited to participate in the online survey between May 2015 and June 2016.
Csiro researchers then used this information to create a detailed picture of the country's eating habits.
The closest Australians got to meeting official dietary guidelines was in the “fruit” food group where 49% of respondents said they met the recommended intake—though that means over half the population still have room to improve.
Of greater concern is dietary performance in regard to discretionary, or junk foods.
Just 1% of Australians are abstaining from junk food, while more than a third admitted to eating more than the recommended maximum allowance.
"We find that there is often a tendency to under-report on certain types of food, so in all likelihood that figure is even higher," Prof. Noakes said.
The report showed that women have slightly better nutritional levels than men.
Construction workers were among those with the poorest diets, while public servants, estate agents and health industry workers reported some of the healthiest eating patterns.
The report also tracked food avoidance in diets for the first time, and found that approximately one in three Australian adults avoid one or more foods such as gluten, dairy or meat.
"It is never too late to eat better and increase your score, and the nation's," Prof Noakes added.